Bottom Line:
These properties are critical for electrical detection of tissue health and viability in applications such as toxicological screening.By applying uniform white noise at the gate of an organic electrochemical transistor (OECT), and measuring the resulting current noise, we are able to dynamically monitor the impedance and thus integrity of cultured epithelial monolayers.We show that noise sourcing can be used to track rapid monolayer disruption due to compounds which interfere with dynamic polymerization events crucial for maintaining cytoskeletal integrity, and to resolve sub-second alterations to the monolayer integrity.

ABSTRACTImpedance sensing of biological systems allows for monitoring of cell and tissue properties, including cell-substrate attachment, layer confluence, and the "tightness" of an epithelial tissue. These properties are critical for electrical detection of tissue health and viability in applications such as toxicological screening. Organic transistors based on conducting polymers offer a promising route to efficiently transduce ionic currents to attain high quality impedance spectra, but collection of complete impedance spectra can be time consuming (minutes). By applying uniform white noise at the gate of an organic electrochemical transistor (OECT), and measuring the resulting current noise, we are able to dynamically monitor the impedance and thus integrity of cultured epithelial monolayers. We show that noise sourcing can be used to track rapid monolayer disruption due to compounds which interfere with dynamic polymerization events crucial for maintaining cytoskeletal integrity, and to resolve sub-second alterations to the monolayer integrity.

f2: Application of noise-based impedance sensing to toxicology.a. Time-frequency spectrogram of transconductance (top; red high, blue low), and snapshots of transconductance vs. frequency upon addition of 8 μM Cytochalasin B (at t = 2.5 min, dashed lines) to media of MDCK I cells cultured on an OECT. b. Time-frequency analysis (red high, blue low) and snapshots of the simultaneously acquired impedance data (/Z/). The snapshots at time t = 0 min are blue, at t = 14 min are red. Black traces are from harmonic frequency sweep measurements before and after the continuous noise experiment. The dotted grey lines are data from the device alone (no cells). c. Cell layer resistance and capacitance of impedance data stitched from drain current and gate current recordings from a single experiment, and fit to the equivalent circuit shown on the right. Black symbols are from harmonic frequency sweep data, while blue-red data are from the noise results in (a,b).

Mentions:
We began the noise experiment (t = 0 min), and added 8 μM of Cytochalasin B at t = 2.5 min. The transconductance and impedance can be visualized using a time-frequency spectrogram (Fig. 2a,b), or by averaging over short time windows (in this case ~10 s) to extract gm and /Z/ curves like those in Fig. 1c,d. At such concentrations of toxin, a readily observable change in the barrier properties is measured over a 4 min duration. By comparison, a typical frequency sweep takes 1–2 min, which would limit the entire measurement of affected barrier function to only a few points that are likely skewed by rapid changes during the sweep of applied frequencies. The results in Fig. 2 are from a single representative noise experiment, which was performed multiple times (Supplementary Figure S3) showing similar dynamics and magnitudes of variation. The control experiments, where addition of cell culture media and DMSO (the Cytochalasin B solvent) are dynamically monitored using noise, are included as Supplementary Figure S4).

f2: Application of noise-based impedance sensing to toxicology.a. Time-frequency spectrogram of transconductance (top; red high, blue low), and snapshots of transconductance vs. frequency upon addition of 8 μM Cytochalasin B (at t = 2.5 min, dashed lines) to media of MDCK I cells cultured on an OECT. b. Time-frequency analysis (red high, blue low) and snapshots of the simultaneously acquired impedance data (/Z/). The snapshots at time t = 0 min are blue, at t = 14 min are red. Black traces are from harmonic frequency sweep measurements before and after the continuous noise experiment. The dotted grey lines are data from the device alone (no cells). c. Cell layer resistance and capacitance of impedance data stitched from drain current and gate current recordings from a single experiment, and fit to the equivalent circuit shown on the right. Black symbols are from harmonic frequency sweep data, while blue-red data are from the noise results in (a,b).

Mentions:
We began the noise experiment (t = 0 min), and added 8 μM of Cytochalasin B at t = 2.5 min. The transconductance and impedance can be visualized using a time-frequency spectrogram (Fig. 2a,b), or by averaging over short time windows (in this case ~10 s) to extract gm and /Z/ curves like those in Fig. 1c,d. At such concentrations of toxin, a readily observable change in the barrier properties is measured over a 4 min duration. By comparison, a typical frequency sweep takes 1–2 min, which would limit the entire measurement of affected barrier function to only a few points that are likely skewed by rapid changes during the sweep of applied frequencies. The results in Fig. 2 are from a single representative noise experiment, which was performed multiple times (Supplementary Figure S3) showing similar dynamics and magnitudes of variation. The control experiments, where addition of cell culture media and DMSO (the Cytochalasin B solvent) are dynamically monitored using noise, are included as Supplementary Figure S4).

Bottom Line:
These properties are critical for electrical detection of tissue health and viability in applications such as toxicological screening.By applying uniform white noise at the gate of an organic electrochemical transistor (OECT), and measuring the resulting current noise, we are able to dynamically monitor the impedance and thus integrity of cultured epithelial monolayers.We show that noise sourcing can be used to track rapid monolayer disruption due to compounds which interfere with dynamic polymerization events crucial for maintaining cytoskeletal integrity, and to resolve sub-second alterations to the monolayer integrity.

ABSTRACTImpedance sensing of biological systems allows for monitoring of cell and tissue properties, including cell-substrate attachment, layer confluence, and the "tightness" of an epithelial tissue. These properties are critical for electrical detection of tissue health and viability in applications such as toxicological screening. Organic transistors based on conducting polymers offer a promising route to efficiently transduce ionic currents to attain high quality impedance spectra, but collection of complete impedance spectra can be time consuming (minutes). By applying uniform white noise at the gate of an organic electrochemical transistor (OECT), and measuring the resulting current noise, we are able to dynamically monitor the impedance and thus integrity of cultured epithelial monolayers. We show that noise sourcing can be used to track rapid monolayer disruption due to compounds which interfere with dynamic polymerization events crucial for maintaining cytoskeletal integrity, and to resolve sub-second alterations to the monolayer integrity.